1. Field of the Invention
The present invention generally relates to a semiconductor device, and more specifically, it relates to a semiconductor device improved to be capable of implementing an excellent wiring circuit and obtaining a highly integrated semiconductor circuit.
2. Description of the Background Art
Following refinement of a semiconductor device, a wire having low resistance and high reliability must be formed in a wiring step. Copper (Cu) is listed as a material satisfying such requirement for the wire. However, copper diffuses into a conductive impurity region formed on a semiconductor substrate from a copper wire connected to the impurity region, to deteriorate diffused junction. Thus, it is difficult to form an excellent impurity region and an excellent wire including a desired connection hole.
A conventional method of fabricating a semiconductor device is now described with reference to FIG. 6.
Referring to FIG. 6, an impurity region 102 is selectively formed on the surface of a semiconductor substrate 101. An insulating layer 103 of silicon oxide is formed by CVD (chemical vapor deposition) in a thickness of 500 to 1500 nm, for example, to cover the surface of the semiconductor substrate 101. Thereafter the insulating layer 103 is patterned by photolithography and etching, for forming a connection hole 104 vertically passing through the insulating layer 103. Further, a trench 105 for defining a wiring layer is formed in the surface of the insulating layer 103 by photolithography and etching, to cover the upper portion of the connection hole 104.
Then, the inner wall surface and the bottom surface of the trench 105 as well as the inner wall surface and the bottom surface of the connection hole 104 are covered with a barrier metal film 106 by PVD (physical vapor deposition) or the like. Thereafter a copper wire 107 serving as a conductive film is embedded in the trench 106 and the connection hole 104.
Then, excess parts of the copper wire 107 and the barrier metal film 106 other than those located on the trench 106 are removed from the upper surface of the insulating layer 103. Thus, the copper wire 107 is completed.
Another conventional method of fabricating a semiconductor device is described with reference to FIG. 7.
A semiconductor substrate 101 selectively formed with an impurity region 102 is prepared. An insulating layer 103 of silicon oxide is formed by CVD in a thickness of about 500 to 1500 nm, for example, to cover the surface of the semiconductor substrate 101. Thereafter the insulating layer 103 is patterned by photolithography and etching for forming a connection hole 104 vertically passing through the insulating layer 103. Then, a barrier metal film 108 is formed on the inner wall surface and the bottom surface of the connection hole 104 by CVD or PVD, and a tungsten film 109 is thereafter embedded in the connection hole 104 by CVD. Then, excess parts of the tungsten film 109 and the barrier metal film 108 are removed from the upper surface of the insulating layer 103 by dry etching or CMP. Thus, a plug filled up with tungsten is formed.
Then, a silicon oxide film 110 is formed on the insulating layer 103 in a thickness of 500 to 1500 nm, for example. Thereafter the silicon oxide film 110 is patterned by photolithography and etching for forming a trench 111 for defining a wiring layer to expose the connection hole 104.
Then, a barrier metal film 112 is formed on the overall surface of the semiconductor substrate 101 by PVD, to cover the inner wall surface and the bottom surface of the trench 111. Thereafter a copper wire 113 serving as a conductive film is embedded in the trench 111 by plating. Then, excess parts of the copper wire 113 and the barrier metal film 112 are removed from the upper surface of the silicon oxide film 110 by dry etching or CMP. Thus, the copper wire 113 is completed.
The conventional semiconductor device is fabricated in the aforementioned manner.
In the semiconductor device shown in FIG. 6, however, it is difficult to form the barrier metal film 106 in a thickness sufficient for preventing diffusion of copper from the copper wire 107. Therefore, copper disadvantageously diffuses into the impurity region 102 from the copper wire 107 to deteriorate diffused junction between the impurity region 102 and the semiconductor substrate 101.
The semiconductor device shown in FIG. 7 has been proposed in order to solve this problem. According to this prior art, a tungsten plug can be formed in the connection hole 104 while the barrier metal film 112 having a sufficient thickness can be formed on the bottom of the connection hole 111, whereby the copper wire 107 can be prevented from diffusion of copper. However, this method requires steps of forming the barrier metal film 108 and forming the tungsten film 109 as well as a CMP removal step for removing the excess parts of the barrier metal film 108 and the tungsten film 109 other than those located on the connection hole 104 from the upper surface of the silicon oxide film 103. In this method, therefore, the number of process steps is increased beyond the number of steps in the method of fabricating the semiconductor device shown in FIG. 6, to disadvantageously reduce productivity.
The present invention has been proposed in order to solve the aforementioned problems, and an object thereof is to provide a semiconductor device improved to be capable of efficiently preventing diffusion of copper from a copper wire.
Another object of the present invention is to provide a semiconductor device not reduced in productivity.
A semiconductor device according to a first aspect of the present invention comprises a semiconductor substrate. An impurity region is formed on the surface of the aforementioned semiconductor substrate. An insulating layer is provided on the aforementioned semiconductor substrate to cover the aforementioned impurity region. A trench for defining a wiring layer is provided on the surface of the aforementioned insulating layer. A connection hole connecting the aforementioned trench and the aforementioned impurity region with each other is provided in the aforementioned insulating layer. A conductive layer made of a high melting point metal and/or a compound thereof is embedded in the aforementioned connection hole. A wiring layer is formed in the aforementioned trench to be electrically connected to the aforementioned conductive layer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.